Method and apparatus for growing multiple crystalline ribbons from a single crucible

ABSTRACT

Methods and apparatus for concurrent growth of multiple crystalline ribbons from a single crucible employ meniscus shapers to facilitate continuous growth of discrete and substantially flat crystalline ribbons having controlled width.

TECHNICAL FIELD

[0001] The invention generally relates to crystal growth. Moreparticularly, the invention relates to methods and apparatus for growingcrystalline ribbons of semiconductors materials.

BACKGROUND OF THE INVENTION

[0002] Silicon sheet material or ribbon is particularly important inmaking low cost solar cells. Continuous growth of silicon ribbonobviates the need for slicing of bulk produced silicon to form wafers.In U.S. Pat. Nos. 4,594,229; 4,627,887; 4,661,200; 4,689,109; 6,090,199;6,200,383; and 6,217,649, continuous silicon ribbon growth is carriedout by introducing two strings of high temperature material up through acrucible that includes a shallow layer of molten silicon. The stringsserve to stabilize the edges of the growing ribbon. The molten siliconfreezes into a solid ribbon just above the molten layer. U.S. Pat. Nos.6,090,199 and 6,217,649 describe a method and apparatus for continuousreplenishment of the feedstock material in a continuous silicon ribbon.As presently practiced, a single ribbon is grown out of a singlecrucible, with each ribbon machine having one such crucible. FIG. 1illustrates this process.

[0003] In order to produce lower cost solar cells and hence expandlarge-scale electrical applications of solar electricity, it isimportant to have lower cost substrate materials for making the solarcell. The current invention provides new and improved methods andapparatus for growing silicon ribbons.

SUMMARY OF THE INVENTION

[0004] Methods and apparatus for concurrent growth of multiple ribbonsfrom a single crucible have been developed. These techniques allow forefficient and low cost growth of silicon solar cell manufacturing.

[0005] In one aspect, the invention features a method for continuouslygrowing multiple semiconductor ribbons concurrently in a singlecrucible. A crucible is provided that has multiple meniscus shapers thatare disposed in a spaced relationship. A melt is formed in the cruciblefrom a semiconductor material. The multiple meniscus shapers separatethe melt into a plurality of distinct melt subregions. Multiple pairs ofstrings are arranged relative to the multiple meniscus shapers. Eachpair of strings (i) has a fixed distance therebetween, (ii) emerges fromone of the distinct melt subregions, and (iii) defines a pair of edgesof a meniscus and controls the width of a ribbon. The multiple pairs ofstrings are continuously pulled away from a surface of the melt to formmultiple discrete and substantially flat semiconductor ribbons.

[0006] In another aspect, the invention features a method for minimizinginterference due to meniscus interactions between adjacent ribbons in amultiple semiconductor ribbon growth system. A melt is formed from asemiconductor material disposed in an open crucible. The melt ispartitioned into a plurality of distinct melt subregions by disposing aplurality of meniscus shapers in the crucible. Each melt subregion has adistinct melt surface defined by a meniscus shaper. Multiplesemiconductor ribbons are continuously grown from the crucible. Each ofthe ribbons is grown from a melt subregion by pulling a pair of spacedstrings away from a distinct melt surface.

[0007] In yet another aspect, the invention features an apparatus forcontinuously growing multiple semiconductor ribbons concurrently in asingle crucible. The apparatus includes a crucible for holding a melt ofa semiconductor material; multiple meniscus shapers arranged in a spacedrelationship in the crucible to partition the melt into a plurality ofdistinct melt subregions; multiple pairs of strings; and multipleafterheaters. Each pair of strings is disposed relative to one of themultiple meniscus shapers. Each pair of strings (i) has a fixed distancetherebetween, (ii) emerges from one of the melt subregions, (iii)defines a pair of edges of a meniscus, and (iv) defines a width of oneof the multiple semiconductor string ribbons as the pair of strings ispulled from the melt subregion. Each afterheater is disposed adjacent asurface of at least one of the semiconductor string ribbons to controlthe thermal profiles of the semiconductor string ribbons.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008]FIG. 1A is a schematic illustration of an embodiment of asingle-ribbon growth system.

[0009]FIG. 1B is a schematic illustration of an embodiment of asingle-ribbon growth system.

[0010]FIG. 2A is a schematic illustration of an embodiment of atwo-ribbon growth system.

[0011]FIG. 2B is a schematic illustration of an embodiment of atwo-ribbon growth system including afterheaters.

[0012]FIG. 2C is a schematic illustration of an embodiment of atwo-ribbon growth system.

[0013]FIG. 3A is a schematic illustration of an embodiment of atwo-ribbon growth system including two meniscus shapers.

[0014]FIG. 3B is a schematic illustration of an embodiment of atwo-ribbon growth system including two meniscus shapers andafterheaters.

[0015]FIG. 3C is a schematic illustration of an embodiment of a meniscusshaper.

[0016]FIG. 4 is a schematic illustration of the effect of meniscus shapeas a function of ribbon spacing in a multiple-ribbon growth system.

[0017]FIG. 5 is a schematic illustration of a two-ribbon growth systemhaving a head-to-tail configuration.

[0018]FIG. 6 is a schematic illustration of an embodiment of anine-ribbon growth system.

DESCRIPTION

[0019] The invention features techniques for the continuous andconcurrent growth of multiple semiconductor ribbons from a singlecrucible, i.e., from one crystal growth machine. The method andapparatus described herein allow for a substantially increasedproduction rate and efficiency and a substantial decrease in capital,material, and labor costs associated with the ribbon growth process by afactor that is virtually equal to the number of ribbons produced permachine. For example, using a double ribbon growth system in which tworibbons are concurrently grown in the same crucible reduces by half thecosts associated with the process (except for the feedstock silicon andstring). In addition, the output measured in terms of amount of ribbonarea per unit time, i.e., the so-called areal output, can besubstantially increased, allowing large scale production in a short timewithout requiring additional equipment.

[0020] In one aspect, the invention generally relates to a method forcontinuously growing multiple semiconductor ribbons concurrently in asingle crucible. Two principal factors connected with growing multiplestring ribbons from a single crucible are (1) the uniformity of thermalgradient from ribbon to ribbon and possible asymmetries associated withmultiple ribbon growth and (2) meniscus interactions between theadjacent ribbons. The methods and apparatus of the invention take intoconsideration each of these factors to allow concurrent growth ofmultiple ribbons that are discrete and substantially flat in a singlecrucible. In the growth of a silicon ribbon, the silicon is subjected tovertical thermal gradients on the order of several hundred ° C./cm as itcools from its melting temperature of about 1412° C. The lack ofductility in silicon and the non-zero second derivative of the coolingcurve can result in large stresses in the ribbon and make it difficultto grow a flat and wide ribbon.

[0021] Some of the stress is relieved by the formations of dislocationsin the crystal structure and/or by buckling growth out of the ribbonplane. Buckling of ribbon results in non-flat ribbons, which areundesirable for solar cell applications. To facilitate flat ribbongrowth, the cooling profile (measured along the growth axis) can betailored to minimize the stress, such as by using an afterheater(sometimes called a radiation shield). U.S. Pat. No. 4,627,887, FIG.13A, shows an example of radiation shields. The afterheater design canalso influence the residual stress in the grown ribbon. Lower stressribbons can typically be processed with higher yields.

[0022] A conventional string ribbon growth method is shown in FIG. 1A. Acontinuous ribbon growth system 10 includes a crucible 11 having thereina melt 12 of silicon and a pair of strings 15 extending through thecrucible 11. A crystalline ribbon of silicon 17 is slowly drawn from themelt 12 as the cooler liquid silicon crystallizes at the top of themeniscus 19. The strings 15 passing through holes (not shown) in thebottom of the crucible 11 become incorporated in and define the edgeboundaries 18 a and 18 b of the crystalline ribbon 17. The strings 15stabilize the edges 18 a and 18 b as the ribbon 17 grows. The surfacetension of the silicon prevents leaks through the holes of the crucible11 where the strings 15 pass through. In the continuous growth system10, the crucible 11 and the melt 12 may be housed within an inertgas-filled housing (not shown) to prevent oxidation of the moltensilicon.

[0023]FIG. 1B shows a schematic cross-sectional view of the stringribbon growth system shown in FIG. 1A. The shape of the meniscus 19 andthe vertical position of its attachment to the ribbon (at thesolid-liquid interface, i.e., the interface of the melt 12 and theribbon 17) is determined primarily by physical constants (Laplace'sequation), the nominal depth of melt in the crucible, and weakly by thesides 13 of the crucible 11. The degree of coupling of the ribbon'smeniscus 19 and the crucible wall is related to the physical distanceseparating the ribbon from the crucible sides 13. Afterheaters orradiation shields 14 are symmetrically deployed on either side of agrowing ribbon 17 to modify the vertical thermal profile and to promotethe growth of low-stress ribbons. For a single ribbon growth such asthat illustrated in FIG. 1A, the afterheater may be disposed on eitherside of a growing ribbon in a symmetrical arrangement as illustrated inFIG. 1B.

[0024] For multiple ribbon growth from a single crucible, there is ageometric asymmetry that leads to a thermal asymmetry in the radiativeflux, as discussed below.

[0025]FIG. 2A shows a continuous two-ribbon dual growth system 20. Thesystem 20 includes a crucible 21 having therein a melt 22 of silicon andtwo pairs of strings 25 a and 25 b extending through the crucible 21.Each of the two pairs of strings 25 a and 25 b has a fixed distancetherebetween and emerge from the melt 22. Two crystalline ribbons 27 aand 27 b of silicon are drawn from the melt 22 as the cooler liquidsilicon crystallizes at the tops of the menisci 29 a and 29 b,respectively. The two pairs of strings 25 a and 25 b passing throughholes (four holes, again not shown, to accommodate two pairs of strings)in the bottom of the crucible 21 become incorporated in and define theedge boundaries of the crystalline ribbons 27 a and 27 b. The two pairsof strings 25 a and 25 b stabilize the edges of the ribbons 27 a and 27b, respectively. The surface tension of the silicon prevents leaksthrough the holes of the crucible 21 where the strings 25 a and 25 bpass through.

[0026] The cross-sectional view of the system shown in FIG. 2A isprovided in FIG. 2B with the addition of afterheaters. The overall widthof the crucible 21 shown in FIGS. 2A and 2B is taken to be the same asthe width of the crucible 11 shown in FIGS. 1A and 1B. The shape ofmenisci 29 a and 29 b and their vertical position at the point ofattachment (at the solid-liquid interfaces, i.e., the interface of themelt 22 and the ribbons 27 a and 27 b, respectively) are determined bythe lateral disposition of the growing ribbons and the sides 23 of thecrucible 21, as well as by the nominal depth of melt in the crucible.There is greater interaction between the menisci 29 b and 29 a with thesides 23 of the crucible 21 than between the meniscus 19 and sides 13 ofthe crucible 11 (shown in FIG. 1A), as the spacing between the ribbonsand the crucible sides is considerably less in the two-ribbon systemdepicted in FIGS. 2A and 2B. Afterheaters or radiation shields 24 aredeployed adjacent the outer surfaces (26 a and 26 b) of the ribbons 27 aand 27 b. As can be seen, there is a potential geometric asymmetry dueto the disposition of afterheaters 24. No afterheaters are deployedadjacent the inner surfaces (26 c and 26 d) of the ribbons 27 a and 27b, as indicated by the dotted region 24 a.

[0027]FIG. 2C shows a top view of the growth system depicted in FIG. 2Aundergoing string ribbon growth. A highly curved meniscus results fromthe growth system of FIG. 2A both at the solid-liquid interface wheregrowth occurs and at the sides of the crucible. A practical limit to thewidth of a crucible for single ribbon growth is such that this meniscusis curved along its entire surface. That is, the distance to thecrucible edge is never great enough to allow for a flat or so-calledfree melt surface. For the single-ribbon crucible, the spacing betweenthe ribbon and the crucible sides is great enough for the interaction tobe weak. In order to realize economic benefits from multi-ribbon growth,it is desirable to reduce this spacing and to minimize the spacingbetween the ribbons. To reduce surface energy, the two menisci betweentwo growing ribbons tend to reduce the surface area between them. In thelimit, this capillary attraction causes the two ribbons to merge intoeach other, rendering multiple ribbon growth impossible. In addition tothe simple capillary attraction described above, a growth instabilityexists that will cause adjacent growing ribbons to tend to merge iftheir respective menisci are allowed to interact. The edges of theribbons still are fixed in position because of the strings present, butmeniscus effects cause the two ribbons to be drawn together andeventually merge at their centers (as shown in FIG. 2C).

[0028] An embodiment of the multi-ribbon growth system according to theinvention is illustrated in FIGS. 3A and 3B. FIG. 3A shows a similarsystem as shown in FIG. 2A except that two meniscus controllers (i.e.,meniscus shapers) 3 a and 3 b are placed around the two pair of strings35 a and 35 b, respectively. The meniscus shapers 3 a and 3 b partitionthe melt 32 to form subregions 3 c and 3 d, respectively. The two pairsof strings 35 a and 35 b are continuously pulled away from the melt 32for two ribbons 37 a and 37 b.

[0029]FIG. 3B is a cross-sectional view of a two-ribbon dual growthsystem 30 as shown in FIG. 3A. FIG. 3C depicts one of the meniscusshapers 3 a in detail. The meniscus shapers 3 a and 3 b allow forcontact with the bulk of the melt through openings 3 e and 3 f at thebottom of the meniscus shapers 3 a and 3 b. The meniscus shapers 3 a and3 b partition the melt 32 to form subregions 3 c and 3 d, respectively,from which two ribbons 37 a and 37 b grow. The tops (3 a′and 3 b′) ofthe meniscus shapers 3 a and 3 b define the menisci 39 a and 39 b,respectively. For the growth of one ribbon (e.g., 37 a), the meniscus 39a is able to act independently of the meniscus 39 b of the nearby ribbon37 b. Thus, in such a configuration, the shape of menisci 39 a and 39 band the vertical position of their attachment to the growing ribbon (atthe solid liquid interface) are now determined by the tops (3 a′ and 3b′) of their respective meniscus shapers 3 a and 3 b and not by theadjacent ribbon (37 a or 37 b) and a more distant crucible side 33.Therefore, the meniscus shapers have the effect of eliminatinginteraction between the adjacent growing ribbons.

[0030] The spacing between the shapers may be varied to fit a particularapplication. Without wishing to be bound by the theory below, theclosest spacing for the meniscus shapers for multiple ribbon growth maybe determined according to the following analysis. Based on the angle ofattachment of the liquid silicon to the growing ribbon is constant atabout 11°, and the density and surface tension of liquid silicon, aswell as an estimate of the height of the interface above the free meltsurface, it is possible to numerically integrate the governing equation(Laplace's equation, below) and step along the meniscus surface for thedesired lateral distance. Successive iterations are performed until therequired boundary conditions are met.

Laplace's equation: p=γ(1/R ₁+1/R ₂)

[0031] where: p is the pressure drop across the interface, γ is surfacetension, and R₁ and R₂ are principal radii of curvature

[0032] This technique yields a family of curves for meniscus shapes as afunction of the dual ribbon spacing as illustrated in FIG. 4. Thesecurves show one half of the meniscus cross section. The extremeleft-hand edge is the surface of the growing ribbon to which themeniscus must attach and the horizontal axis is the distance from thisribbon surface. The vertical axis is the meniscus height above the freemelt surface. Each curve represents a different proposed spacing betweenthe ribbons. By recognizing that a meniscus shaper must intersect thismeniscus in order for the two ribbons to be de-coupled from each other,FIG. 4 can be used as a design tool.

[0033] In one exemplary embodiment, 8 mm wide meniscus shapers or 4 mmon the half-width scale as shown in FIG. 4 are placed with a 0.5 inchribbon spacing, which requires a vertical position of at least 3.5 mmabove the free melt surface. Given some variation in control of the meltdepth in a crucible, this leads to a required height of about 5 mm abovethe free melt surface. Assuming a nominal depth of melt of 4 mm, thisthen gives a meniscus shaper height of 9 mm above the floor of thecrucible. To make multiple ribbon growth viable, it is important tocontrol the melt depth. U.S. Pat. No. 6,200,383 describes a method formelt-depth control.

[0034] The configurations of the pairs of strings may be such that theribbons are grown, for example, in a face-to-face pattern as illustratedin FIGS. 3A-3B, or in a head-to-tail pattern as illustrated in FIG. 5.The configuration may also be a mix of head-to-tail and face-to-face,e.g., a matrix, or other configurations, e.g., a radial configuration,in which ribbons would be disposed to resemble the spokes of a wheel.

[0035] The multiple miniscus shapers may be identical in shape and sizeor different in shape and/or size. The multiple pairs of strings mayalso have different distances between the strings within a pair, therebyallowing concurrent growth of ribbons of different sizes. The ribbonsare typically grown, i.e., pulled, in a direction perpendicular to orsubstantially perpendicular to the melt surface from where the ribbon isgrown. Other growth directions, e.g., angled pulling of strings, may beemployed in certain growth systems to achieve the desired ribbonspecifications.

[0036] The number of ribbons that can be grown from a single cruciblemay be varied according to the applications. In one embodiment, as shownin FIG. 6, nine ribbons are concurrently grown from a single crucible61. Nine meniscus shapers (6 a-6 i) are placed in the crucible 61 toform mine melt subregions (6 a′-6 i′). Each of the nine subregionssupports the growth of a string ribbon. Afterheaters 64 are placedadjacent the outside surfaces (66 a and 66 i) of the two outermostribbons (67 a and 67 i). The inner ribbons (67 b-67 h) have nothingbetween them as indicated by the dotted regions 64 a. For the innerribbons (67 b-67 h) in a face-to-face configuration such as thatdepicted in FIG. 6, the surrounding thermal environment is due primarilyto the adjacent growing ribbons and therefore is very uniform andconstant because each ribbon now is surrounded by constant emissivitysurfaces. In such a case, the adjacent ribbons act as afterheaters foreach other.

[0037] In another aspect, the invention features a method for minimizinginterference between adjacent ribbons in a multiple semiconductor ribbongrowth system. In one exemplary embodiment and referring again to FIGS.3A-3B, meniscus shapers 3 a and 3 b are used to minimize theinterference between adjacent growing ribbons 37 a and 37 b in atwo-ribbon dual growth system. Instead of the adjacent ribbons and sides33 of the crucible 31 determining the menisci 39 a and 39 b, themeniscus shapers 3 a and 3 b provide the edge boundaries for isolatedmelt subregions 3 c and 3 d (each with a distinct melt surface definedby the meniscus shapers), from which two pairs of strings arecontinuously pulled away from the melt and two ribbons are grown.

[0038] Similarly in FIG. 6, meniscus shapers 6 a-6 i are used tominimize the interference between adjacent growing ribbons 67 a-67 i ina nine-ribbon dual growth system. Instead of the adjacent ribbons andsides 63 of the crucible 61 determining the menisci 69 a-69 i, themeniscus shapers 6 a-6 i provide the boundaries for nine isolated meltsubregions (6 a′-6 i′, each with a distinct melt surface defined by themeniscus shapers), from which the nine pairs of strings (not shown) arecontinuously pulled and nine ribbons 67 a-67 i are grown.

[0039] It has now been discovered that ribbon growth is not affected bya geometrical asymmetry in the radiative thermal environment asproduced, for example, by having an afterheater only on one side of theribbon. The thermal resistance of the ribbon through its thickness is solow that symmetry of the radiative environment is not required. Thus,the radiative flux on either side of a growing ribbon can be asymmetricand still allow for successful growth of flat ribbons. This observationis of particular significance for a two-ribbon system as each ribbon“sees” an identical radiative environment.

[0040] An important aspect of the invention is that growth of manyribbons from a single crucible results in a thermal environment for allthe inner ribbons, excluding the two outer ribbons, that is extremelyuniform in time. The uniformity in time can be particularly valuable, asit is well known to one skilled in the art that deposits of siliconoxide or silicon carbyoxide can build up over time on the afterheatersand thereby affect their radiative properties. This in turn can resultin changes in the thermal profile that can make it more difficult toachieve the growth of flat, low stress ribbon.

[0041] The invention also features an apparatus for continuously growingmultiple semiconductor ribbons concurrently in a single crucible.Exemplary embodiments of the apparatus are depicted in FIGS. 3A, 3B and6.

[0042] Referring again to FIG. 3A, one embodiment of a two-ribbon growthsystem 30 includes a crucible 31 for holding a melt 32, meniscus shapers3 a and 3 b for partitioning of the melt surface, string pairs 35 a and35 b placed in the crucible and emerging from the meniscus shapers 3 aand 3 b, respectively, and afterheaters 34 (not shown in FIG. 3A butshown in FIG. 3B) placed adjacent the outer surfaces (26 a and 26 b) ofthe ribbons 37 a and 37 b.

[0043] Referring again to FIG. 6, one embodiment of a nine-ribbon growthsystem 60 includes a crucible 61 for holding a melt 62, meniscus shapers6 a-6 i for partitioning of the melt surface, nine pairs of strings (notshown) placed in the crucible and emerging from the meniscus shapers 6a-6 i, respectively, and afterheaters 64 placed adjacent the outersurfaces (66 a and 66 i) of the ribbons 67 a and 67 i.

[0044] A housing is typically included to isolate from the ambientenvironment the melt and a portion of the solidifying ribbon, especiallythe solid-liquid interface and any part of the ribbon having atemperature of 400° C. or higher. The housing is typically filled withan inert gas, e.g., Argon.

[0045] Sheet materials or ribbons of materials that may be grown usingthe methods and apparatus discussed herein include, e.g., silicon,germanium, silicon carbide, gallium arsenide, gallium phosphide, indiumarsenide, gallium antimonide, indium antimonide, indium phosphide,gallium arsenide antimonide, gallium nitride, ternary compounds, andalloys thereof. The methods and apparatus discussed above can be appliedin multi-ribbon growth systems where two, three, four or more (e.g.,twenty) ribbons are concurrently grown from a single crucible.

[0046] Each of the patent documents disclosed hereinabove isincorporated in its entirety by reference herein. Variations,modifications, and other implementations of what is described hereinwill occur to those of ordinary skill in the art without departing fromthe spirit and the scope of the invention. Accordingly, the invention isnot to be limited only to the preceding illustrative descriptions.

What is claimed is:
 1. A method for continuously growing multiplesemiconductor ribbons concurrently in a single crucible, the methodcomprising providing a crucible having multiple meniscus shapersdisposed in a spaced relationship therein; forming a melt from asemiconductor material disposed in the crucible, the multiple meniscusshapers separating the melt into a plurality of distinct meltsubregions; arranging multiple pairs of strings relative to the multiplemeniscus shapers, each pair of strings (i) having a fixed distancetherebetween, (ii) emerging from one of the distinct melt subregions,and (iii) defining a pair of edges of a meniscus and controlling thewidth of a ribbon; and continuously pulling the multiple pairs ofstrings away from a surface of the melt to form multiple discrete andsubstantially flat semiconductor ribbons.
 2. The method of claim 1wherein the semiconductor material is silicon, germanium, siliconcarbide, or alloys thereof.
 3. The method of claim 1 further comprisingpositioning multiple afterheaters relative to the ribbons wherein eachafterheater is disposed adjacent a surface of at least one of theribbons to control the thermal profiles of the ribbons.
 4. The method ofclaim 1 further comprising arranging the multiple pairs of stringsrelative to the multiple meniscus shapers such that the ribbons aregrown substantially parallel to one another in a face-to-face pattern.5. The method of claim 1 further comprising arranging the multiple pairsof strings relative to the multiple meniscus shapers such that theribbons are grown substantially in a head-to-tail pattern.
 6. The methodof claim 1 further comprising arranging the multiple pairs of stringsrelative to the multiple meniscus shapers such that the ribbons aregrown in a pattern comprising adjacent ribbons in both a face-to-faceand a head-to-tail pattern.
 7. The method of claim 1 wherein themultiple meniscus shapers have identical size and shape.
 8. The methodof claim 1 wherein the multiple meniscus shapers have different size orshape.
 9. The method of claim 1 wherein two to twenty ribbons are grownconcurrently.
 10. The method of claim 1 wherein the distance betweeneach pair of strings varies.
 11. The method of claim 1 furthercomprising pulling the multiple pairs of strings in a directionperpendicular to the melt surface.
 12. The method of claim 1 furthercomprising pulling the multiple pairs of strings in a direction otherthan perpendicular to the melt surface.
 13. A method for minimizinginterference between adjacent ribbons in a multiple semiconductor ribbongrowth system, the method comprising forming a melt from a semiconductormaterial disposed in an open crucible; partitioning the melt into aplurality of distinct melt subregions by disposing a plurality ofmeniscus shapers in the crucible, each melt subregion having a distinctmelt surface defined by the meniscus shaper; continuously growingmultiple semiconductor ribbons, each of the ribbons being grown from amelt subregion by pulling a pair of spaced strings away from thedistinct melt surface.
 14. The method of claim 13 wherein the step ofpartitioning the melt into a plurality of distinct melt subregionscomprises positioning at least one meniscus shaper on the melt surface.15. The method of claim 13 wherein the semiconductor material issilicon.
 16. The method of claim 13 further comprising positioningmultiple afterheaters relative to the ribbons wherein each afterheateris disposed adjacent at least one of the ribbons to control the thermalprofiles of the ribbons.
 17. An apparatus for continuously growingmultiple semiconductor ribbons concurrently in a single crucible, theapparatus comprising a crucible for holding a melt of a semiconductormaterial; multiple meniscus shapers arranged in a spaced relationship inthe crucible to partition the melt into a plurality of distinct meltsubregions; multiple pairs of strings wherein each pair is disposedrelative to one of the multiple meniscus shapers, each pair of strings(i) having a fixed distance therebetween, (ii) emerging from one of themelt subregions, (iii) defining a pair of edges of a meniscus, and (iv)defining a width of one of the multiple semiconductor ribbons as thepair of strings is pulled from the melt subregion; and multipleafterheaters wherein each afterheater is disposed adjacent a surface ofat least one of the semiconductor ribbons to control the thermalprofiles of the semiconductor ribbons.
 18. The apparatus of claim 17wherein each pair of strings pass through a pair of holes in thecrucible.
 19. The apparatus of claim 17 wherein each afterheater isdisposed adjacent an outer surface of a ribbon.
 20. The apparatus ofclaim 17 wherein the distance between the strings of each pair ofstrings varies.
 21. The apparatus of claim 17 further comprising ahousing for isolating from the ambient environment the melt and aportion of the solidifying ribbon comprising a solid-liquid interfaceand having a temperature of 400° C. or higher.
 22. The apparatus ofclaim 17 comprising two to twenty pairs of strings for concurrentlygrowing two to twenty ribbons.